1. Field of the Invention
This invention relates to breathing equipment for aircrew and more particularly to breathing equipment which can be used in conjunction with electronic avionic systems.
2. BACKGROUND OF RELATED ART
Avionic systems used by pilots generally require part of the system to be helmet mounted but the helmet has to be maintained in a fixed position relative to the wearer's head and eyes if the avionics are to work properly.
Another problem with modem breathing equipment used by aircrew is that it has to incorporate means to increase the seal that the facemask with the wearer's face during pressure breathing otherwise the facemask leaks when the breathable gas at the required increased pressure is fed to the interior of the mask. In one prior art arrangement, an inflatable bag is provided at the rear of the pilot's helmet which expands when pressure breathing is required with the result that the helmet moves rearwardly and the facemask connected to it is pulled towards the wearer's face to maintain the required seal therewith. The problem with this arrangement is that the helmet moves relative to the pilot's head so avionics systems cannot be mounted to it as they require a stable mounting platform. Furthermore, as the viewing screen onto which the avionics image is projected must be kept at a fixed distance from the wearer's eyes, it cannot be mounted on a facemask which moves relative to the wearer's face because its position relative to the pilot's eyes will change constantly in response to the pressure of the breathable gas supplied to the facemask.
In our earlier filed patent application referred to above, which has been published under No.PCT/GB91/01034, we overcame the problem of keeping the helmet in a fixed position by mounting the movable facemask within a rigid outer shell attached to the helmet at a fixed distance therefrom and fitting an inflatable bladder between the rigid shell and the facemask which could be inflated to press the periphery of the facemask towards the pilot's face when the pressure of the breathable gas supplied to the interior of the mask and the inflatable bladder increased above that for normal breathing. In another embodiment, the facemask included a re-entrant or bellows section which reconfigured and extended in a direction towards the pilot's face when the pressure of the breathable gas supplied to the interior of the facemask increased above that required for normal breathing.
The significant feature of our earlier breathing system was that the facemask was dynamically movable relative to the pilot's face due to the reaction between the rigid outer shell and the inflatable bladder or between the rigid outer shell and the re-entrant or bellows section incorporated in the facemask. Thus, it was the facemask not the helmet which moved when pressure breathing was required so avionics could be mounted on the helmet.
The problems discussed above are further compounded if the facemask has to be incorporated into a hood to protect the wearer against nuclear, biological or chemical (NBC) agents and also be capable of use with helmet mounted avionics. This is because the distance between the clear visor area provided in the rigid front portion of the hood to enable the wearer to see has to be kept at a fixed distance in relation to the wearer's eyes. This is difficult to achieve in conventional breathing equipment which does not have a dynamically movable facemask as this distance can vary depending on the shape of the wearer's chin. This is a particular problem if night vision glasses (NVG) are to be used because the distance between the wearer's eyes and the NVG is critical and must not vary. Furthermore, when the wearer is subjected to G forces in an aeroplane of up to 9G for instance, the helmet becomes very unstable, particularly if a rear inflatable bladder is used.
The Applicants have now realised that their earlier breathing system can be modified to have a clear viewing screen or visor fitted thereto or incorporated therein onto which images can be projected by avionics systems mounted either on the pilot's helmet or elsewhere in the cockpit as the rigid shell provides a stable non-movable platform to support the screen or visor. It can also be readily adapted for use with an NBC hood including a respirator.